Variable-speed electric drill



Oct. 17, 1950 c, SPARKLIN 2,525,839

VARIABLE-SPEED ELECTRIC DRILL Filed Jan. 31, 1946 2 Sheets-Sheet 2""ljil all/ill,

Patented Oct. 17, 1950 VARIABLE-SPEED ELECTRIC DRILL Charles H.Sparklin, Chicago, Ill., assignor to Birtman Electric Company, acorporation of Illinois Application January 31, 1946, Serial No. 644,509

4 Claims.

This invention relates to a variable speed electric drill, andparticularly to a portable hand drill.

Electric drills of the portable type have not heretofore beenconstructed wherein the speed is variable over a wide range. In mostvariable speed electric drills the speed range is rather narrow, and thetransfer from one speed to an other is rather erratic. speed is notsmooth and constant for any given setting of the speed controlmechanism, and there has been no simple means of locking the mechanismat one predetermined speed. In the prior drills it has also beendifficult to hold the drill steady, as the fingers of the operator hadto always engage the speed control trigger or other mechanism.

I have invented a variable speed electric drill wherein the speed can beregulated over a wide range. The control trigger may be set for anydesired speed and locked in position so that this speed will bemaintained. The drill operates smoothly and efficiently, and a changefrom one speed to another is easily accomplished. In the new drill thereis no need to manually hold the control trigger to any desired position,and the speed can be changed by the action of one finger, usually thesecond finger, while the index finger and the others are used to holdthe drill steady.

The locking mechanism that holds the triggerin its desired position maybe readily released. In one embodiment of the invention the index fingerof the operator is used to hold the drill steady, the second finger isused to regulate the speed, while the third finger is used to releasethe lock mechanism.

The invention will be described as related to the embodiment set out inthe accompanying drawings. Of the drawings Fig. 1 is a vertical sectiontaken through a variable speed hand drill embodying the invention; Fig.2 is a fragmentary elevation of the top portion of the drill partiallybroken away for clarity of illustration; and Fig.

3 is a horizontal section taken along line 3-3 of Fig. 1. Figure 4 is anelevation of the centrifugally responsive members.

The drill shown in the accompanying drawings comprises a housing ill, amotor armature l2, field windings [3, a pinion I 4 at the lower end ofthe shaft H and operating against a circular 1 gear [5, a drill chuck l6rotated by the gear IS, a speed governor H at the upper end of the shaftI l, and a trigger l8 for operating the speed governor.

The speed governor I! is shown and described In these prior drills theshaft.

2 in my copending application, Serial No. 580,114, filed February 28,1945. The speed governor comprises rotatable plates [9 and 20 mounted onthe upper end of the motor shaft II with the plates holding bell cranks2| at right angles to the plates. As described in the above applicationthe plates i9 and 20 hold rotatably mounted arms that are movableoutwardly under centrifugal force. As these arms move outwardly theyoperate through bell cranks 2| to force the thimble 22 in a generallyoutward direction. The, distance that the thimble is moved outwardlydepends upon the speed of rotation of the motor The construction of thisportion of the speed governor and its operation are described fully inthe above copending application. The thimble 22 operates against acontact button 23 on a switch arm 24. This outer switch arm 24 isarranged generally parallel to an inner switch arm 25 with the thimble22 extending through the inner switch arm 25. Both switch armsarerotatably mounted around a common fulcrum pin 26 and have contactpoints 21 and28 on their other.

ends. These contact points are urged together under the force of aspring 2$located around the fulcrum pin 26. The free end ofthe, innerswitch arm 25 is provided with a U-shaped eX-.

tension 30 which presses against the top portion of the trigger I8. Theswitch arm 25 is held in contact with the trigger. by means of. a spring3| extending between the portion 30 and the flat base of the pistol gripportion 32 of the housing.

The trigger l8 rests against an extension 33 of the housing when thetrigger is in its ofi position. This extension is engageable with theindex finger of the operator to hold the drill steady. The second fingerof the operator is engageable with a depressed portion 34 of the triggerl8.

In order to lock the trigger [8 in any desired position holding meansare provided. This holding means may have any form desired, and as showncomprises a serrated outer surface 35 on the trigger 18 that is engagedby serrationson a rockably mounted lever 36. This lever is mounted onthe pistol grip portion 32 of the housing and the two sets of serrationsare held in engaging relationship by a short spring 31 urging the upperend of the lever 36 outwardly.

The variable speed drill is provided with the usual electric lead wire38 leading into the housing and other wires 39 and 40 leading to thecontact points 24 and 25. If desired a condenser (not shown) may beprovided between the contact points 21 and 28. The motor is provided 3with the usual armature 4|, brushes 42, brush holders 43, and motorshaft bearings 44 and 45.

When the trigger I8 is in its lowest position as shown in Fig. 1 thecontact points 2'! and 28 are held apart by compression spring 3|. Whena drill is to be operated the operator grasps the pistol grip 32 andwraps his index finger around the extension 33, his second finger aroundthe depressed portion 34 of the trigger l8, and his other fingers aroundthe pistol grip 32. The third finger may be used to control the lockinglever 36. When it is desired to start the drill the operator, using hissecond finger, pulls the trigger l8 upwardly a short distance. Thiscloses the contact points 21 and 28 and starts the drill operating atlow speed. If a higher speed is desired the trigger i8 is moved to ahigher position. When the trigger is pulled upwardly as far as it willgo the drill will be operating at its highest speed. This position isshown in dotted lines on Fig. 1. The trigger i8, and thus the speedcontrol mechanism, may be locked in any position by the lever 36engaging the serrations 35 on the trigger. When it is desired to changepositions the third finger will be used to relieve the lever 36, and thetrigger may be moved to a new po- ;sition. In the embodiment shown,therefore, the operator holds the drill steady with his thumb, indexfinger, palm, and last two fingers. The second finger may be used tooperate the trigger .l8. When it is desired to change speeds the thirdfinger may be used to disengage the lever .36.

Having described my invention as related to th embodiment shown in theaccompanying \drawings, it is my intention that the invention be notlimited by the deails of description unless (otherwise specified, butrather be construed ibroadly within its spirit and scope as set out inthe accompanying claims.

I claim:

1. In a variable speed electric drill comprising a motor, a motor shaftextending beyond the motor, a rotatable plate member attached to one endof said shaft, a sliding member on said end of said shaft, means on theplate member for urging the sliding member outwardly a distancedependent upon the speed of rotation of the plate member, generallyparallel switch arms located beyond the upper end of the shaft andpivotally 4 mounted about a common fulcrum at one end of said arms,contact points at the other ends of said arms, said sliding memberextending through the inner arm and contacting the outer arm, springmeans normally urging the two arms together, and second spring meansnormally urging the inner arm toward the motor: positioning meansoperating on the contact end of the inner arm to position both armsrelative to the upper end of the shaft.

2. The electric drill of claim 1 wherein the positioning means comprisesa finger-operated trigger member and means for locking said triggermember in a predetermined position.

3. The electric drill of claim 1 wherein the drill is provided with ahousing including a pistol grip including a holding portion capable ofbeing grasped by the index finger of the operator, and the positioningmeans comprises a trigger member slidable on said housing and abuttingagainst said holding portion when the trigger member is in one position,said trigger member being capable of being operated by the second fingerof the operator, and there are provided readily releasable locking meansfor locking the trigger member in a predetermined position.

4. The electric drill of claim 1 wherein the positioning means comprisesa finger-operated trigger member, and means for locking said triggermember in a predetermined position, said contact points being separatedfrom each other when the trigger member is in an off position.

CHARLES H. SPARKLIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,489,182 Weinberg Apr. 1, 19241,690,103 Clark Nov. 6, 1928 1,827,372 Riddell Oct. 13, 1931 2,103,589Lee et al Dec. 28, 1937 2,228,801 Wilhide Jan. 14, 1941 2,263,136 Knouseet al. Nov. 18, 1941 2,353,314 Lee July 11, 1944 2,406,389 Lee Aug. 27,1946 2,442,456 Boyden et al. June 1, 1948

